This invention relates generally to large storage tank inlet and/or outlet fittings and more particularly to double wall polyolefin tank combination inlet/outlet fittings with expansion and contraction capability.
Flexible inlet/outlet fittings generally used with above ground storage vessels utilizing double wall containment often include a tubular connector to which external plumbing connections may be made to allow fluid to be pumped into and withdrawn from the storage tank. The inlet and/or outlet fitting may be plastic or metal. In some cases where metal fittings are used they may be substantially encased in plastic for protection from any corrosive chemicals that may be stored within the vessel or tank.
In the past, plastic or polyolefin storage tanks were not generally encased within a second tank or containment to insure against leakage. Therefore, polyolefin tanks were generally fitted with plastic or metal inlet/outlet fittings or with metal pipe flanges encased in plastic for providing fluid ingress or egress to the interior of the vessel or tank. With the proliferation of double wall or secondary containment vessels, it becomes more difficult to make a proper connection seal when penetrating both vessel walls. In most cases, pipes are usually positioned in an aperture that passes through the inner and outer walls of the vessels and secured thereto. The pipe is usually bonded to the walls of the tank or otherwise attached by plastic flanges to secure the pipe to the vessel walls.
In other applications, inlet and outlet pipes pass through a reservoir formed on the exterior of the tank to contain leaked fluid. In these applications the pipe is usually exposed to the corrosive environment to which the storage tank is exposed thereby precluding the use of metal pipe unless fully encased in a polymeric coating impervious to the chemicals involved. This frequently results in leaks or corrosion damage to the metal pipe and its fittings. In many cases where a secondary reservoir is used for leak protection, leaks can occur at the joints between the double walls of the reservoir around the pipe or pipefittings. Obviously, any type of leak can create a great deal of difficulty with a storage tank and limit the useful life of the vessel. More recent polyolefin storage tanks are made of reinforced plastic to resist the corrosive environment generally associated with harsh chemicals. Therefore, it becomes more essential that the inlet and outlet fittings and tubular connected thereto be compliant with the vessel specification.
Problems also occur when very large, dual wall plastic tanks are used. Such problems include misalignment of the inlet/outlet openings in the vessel that makes securing a fitting to each of the vessel walls very difficult.
Further, expansion, contraction, and flexing of the tank walls tend to break the seals around the inlet/outlet flanges. Where metal flange bolts are used to secure the fittings to tank walls, bolt heads are often eaten away as a result of corrosive chemicals in the tanks, thereby causing leakage. Therefore, it is highly desirable to have a more flexible fitting arrangement for penetrating polyolefin double wall tanks, as would the use of plastic pipe, plastic encapsulated fittings, and associated hardware. A flexible fitting is therefore required that would compensate for differential expansion and contraction of the inner and outer vessel walls.
The double wall tank or vessel fitting of the present invention is generally described as a series of elements including a pipe flange attachable externally to the inner vessel side wall by a plurality of bolts having plastic encapsulated heads inserted from the inside of the inner vessel wall and through apertures provided in the pipe flanges and secured thereto by nuts and washers. The fitting composition further includes a flexible containment fitting having a corrugated wall and circular flanges at each end, one end of which is attached to the exterior of the outer tank or containment vessel with similar bolts having encapsulated heads located between the walls of the two vessels. A pipe extending from the socket portion of a pipe flange attached to the exterior wall of the inner vessel extends through the flexible containment fitting and is captured therein by an external pipe flange fitting secured to the external end of the flexible containment fitting, the external flange fitting having a socket portion for receiving the pipe as necessary to accommodate fitting make-up. Compensation for deflection, alignment, and expansion of the inner vessel relative to the external containment vessel is absorbed by the flexible containment-fitting element.